As an example of a narrowband deployment with a GSM-based network, a proposed standard for IS-136HS integrates 200 kHz GSM-like carriers with the current IS-136 TDMA system, with a 1 MHz initial deployment. General reference to GSM carriers, networks and mobile stations can be had by referring to “The GSM System for Mobile Communications”, by Michel Mouly and Marie-Bernadette Pautet, 1992, the disclosure of which is incorporated by reference in its entirety.
One attractive solution would be to use the nearly completed specification, at the time of filing of the Provisional Patent Application, for Enhanced General Packet Radio Services, or EGPRS having 8-PSK modulation plus General Packet Radio Services (GPRS) packet data channels, from GSM/ETSI. This would save a considerable amount of specification work by adapting the work already done for the GSM 200 kHz carrier. However, at least some network operators have expressed a preference to make the initial 200 kHz deployment using a very narrow bandwidth (1 MHz), whereas currently used GSM systems require at least 2.5 MHz bandwidth. This is because each cell in a GSM system must transmit a high power, continuous Broadcast Control Channel (BCCH) signal. A mobile station or terminal (e.g., a GSM cellular telephone) uses the BCCH transmission for synchronization and neighbor cell channel monitoring purposes. In addition, all of the network parameters as well as the paging messages are received from the BCCH carrier.
Those skilled in the art will appreciate that the interference from these continuously transmitted BCCH carriers must be somehow reduced, otherwise the introduction of a 200 kHz network into a 1 MHz bandwidth system is very difficult or technically impossible.
A 3-Carrier Compact Solution was adopted at a UWCC.GTF.PDFG/RF-group meeting 13-15.5.99 in Monterey (UWCC.GTF.PDFG/99.04.13.38, 3-Carrier Compact Proposal). The 3-Carrier Compact Solution is a proposal for IS-136HS that maintains a spectrum deployment below 1 MHz. The general idea is to use three carriers (600 kHz) in a ⅓ reuse, but to achieve 9 or 12 reuse for control channels by using a 200 kHz synchronous network. The 3-Carrier Compact Solution was presented to ETSI during a Paris EDGE SMG workshop (Tdoc SMG2 EDGE 122/99, Tdoc SMG2 EDGE 152/99, Tdoc SMG2 EDGE 153/99). Reference in this regard can be had to Appendix A of the above-referenced Provisional Patent Application No. 60/136,494, filed May 28, 1999.
In this proposal the control channel is discontinuously transmitted. As a result, the neighbor channel measurements and neighbor cell base station identity (BSIC) decoding become more difficult when the mobile station is in a traffic mode. However, the IS-136HS compact was developed for GPRS traffic only and, therefore, the mobile station neighbor channel measurement and BSIC decoding capabilities were viewed as sufficient for packet-only services.
However, the inventors have analyzed the neighbor channel measurement and neighbor channel BSIC decoding capability of the 3-Carrier Compact Solution. The results of this analysis are presented in Appendix B of the above-referenced Provisional Patent Application No. 60/136,494, filed May 28, 1999, which has been incorporated by reference herein in its entirety. In brief, the analysis shows that the 3-Carrier Compact Solution proposal has serious problems with delay critical services (including both circuit switched and packet switched services) when the mobile station must handle both uplink and downlink transactions during each GSM TDMA frame. In this case there will be only certain neighbor channel measurement and BSIC decoding positions where the mobile station is able to “see” the neighbor cell signal. Therefore, it has been discovered that the mobile station will not be able to measure a sufficient number of neighbor cells, and will not be able to see a neighbor cell BSIC, without dropping some circuit switched traffic bursts. The necessity to drop traffic bursts in order to make neighbor cell channel measurements is obviously an undesirable solution for a number of reasons.